A 27-year-old female with chronic kidney disease (CKD) presents with fatigue and shortness of breath. Blood tests reveal a low hemoglobin level (7.8 g/dL) and metabolic acidosis. The physician explains that a specific amino acid in hemoglobin plays a key role in buffering blood pH and maintaining oxygen delivery. Which amino acid is responsible for this buffering effect?

A 65-year-old hypertensive male is diagnosed with atherosclerosis and has frequent episodes of angina. His physician prescribes nitroglycerin, which alleviates his chest pain by dilating blood vessels. The physician explains that the drug works by increasing the bioavailability of a molecule derived from an amino acid. Which amino acid is a direct precursor for the synthesis of this molecule?

A 52-year-old male presents with progressive muscle weakness and difficulty swallowing. His history reveals frequent episodes of pneumonia due to aspiration. Laboratory tests show elevated serum creatine kinase (CK), and a muscle biopsy reveals misfolded proteins with abnormal disulfide bond formation. Genetic testing confirms a mutation affecting cysteine residues in a structural protein. Which of the following proteins is most likely affected by the disrupted disulfide bond formation?

A 6-month-old infant with isovaleric acidemia is stable on a leucine-restricted diet and carnitine supplementation. The parents ask about long-term complications and monitoring. Which of the following is the most important long-term monitoring parameter for this patient?

A 2-week-old infant with known isovaleric acidemia is brought to the emergency department with vomiting, lethargy, and tachypnea. Blood gas analysis reveals severe metabolic acidosis. What is the most appropriate immediate management for this patient?

A 9-month-old boy with a history of recurrent vomiting, developmental delay, and metabolic acidosis is diagnosed with isovaleric acidemia. The pediatric metabolic specialist discusses a long-term treatment plan with the parents. Which of the following is the most effective long-term management strategy for this child?

A 2-week-old infant presents with vomiting, poor feeding, lethargy, and irritability. The parents mention that the baby’s urine has a ‘sweaty feet’ odor. Laboratory tests reveal high anion gap metabolic acidosis and hyperammonemia. A metabolic workup confirms the diagnosis of an organic acidemia. Which enzyme is deficient in this disorder?

A 3-day-old newborn is brought to the emergency department due to poor feeding, lethargy, and vomiting. The baby was born at term via an uneventful vaginal delivery. On examination, the infant is hypotonic, with tachypnea and a “sweaty feet” odor. Laboratory studies reveal severe metabolic acidosis, anion gap elevation, and hyperammonemia. Newborn screening results show elevated C5-acylcarnitine levels. Which of the following tests would most likely confirm the diagnosis?

A 3-day-old newborn presents with poor feeding, vomiting, lethargy, and a “sweaty feet” odor. Laboratory tests reveal metabolic acidosis, hyperammonemia, and elevated urinary organic acids. What is the most likely diagnosis?

A 45-year-old woman presents with joint pain, skin fragility, and delayed wound healing. Her physician suspects a connective tissue disorder and orders a collagen biosynthesis analysis. The results indicate a defect in hydrophobic amino acids important for collagen stability. Which of the following amino acids is MOST important for collagen formation and structural integrity?